In applicant's patent, U.S. Pat. No. 4,928,030 issued May 22, 1990, he teaches two- and three-axis piezoelectric actuators that position an object such as a rod or motor shaft by walking traction. A lifter piezoelectric actuator portion positions the actuator's traction member perpendicular to the object's surface. A tangenter piezoelectric actuator portion positions the actuator's traction member tangential to the object's surface. Lifter and tangenter portions of an actuator are integrally constructed and independently electrically controllable. Cyclical coordinated lifter and tangenter actions cause the traction member to walk the object's surface in a manner which differs from that of the ultrasonic traveling wave motors referenced infra.
Applicant's patent U.S. Pat. No. 5,043,621 issued Aug. 27, 1991 discloses a walking cycle which consists of activating the lifter to apply a predetermined normal force between the traction member and the object while the tangenter translates the traction member at a speed equal to the surface speed of the object. During application and removal of normal force, no mechanical work is done by the traction member on the object. As the normal force is applied, a tangential strain corresponding to a tangential force on the positioned object is added by the tangenter portion. The product of the tangential force and the tangential distance traveled during the power portion of the stroke is the work done on the object. The work done per unit time, averaged over a complete cycle, is the power transmitted to the object.
At the end of the power portion of the cycle the tangential strain is removed as the normal force is removed by the lifter, still maintaining zero relative speed between object and traction member. As the traction member leaves the object's surface, the traction member retraces, that is, it reverses tangential stroke direction and changes speed until the opposite extreme tangential position is reached, thereby preparing for a new walking stride. This is a smooth walking cycle because sliding is avoided.
When actuators execute walking cycles in pairs, one actuator performs a power stroke while the other retraces. A predetermined coordinated positioning of the traction members of both actuators results in bipedal smooth walking. Smooth walking is defined in U.S. Pat. No. 4,928,030 as uninterrupted and smooth tractional power transmission without sliding.
The piezoelectric materials of U.S. Pat. No. 4,928,030 are generally electrically polarized ferroelectric ceramics. This class of materials is relatively brittle, having relatively little tensile strength. In addition, the temperature above the usual room temperature at which electrical polarization is irreversibly lost, usually called the Curie temperature, is relatively low. These physical properties are a detriment in some applications of walking actuators. U.S. Pat. No. 4,928,030 also teaches the use of relatively high applied voltages to achieve desirably large mechanical strokes. High voltages are a disadvantage in the context of solid state electronic drive devices, such devices having evinced more efficient operation with low voltages with relatively large currents.
Applicant's copending application Ser. No. 07/743,069 filed Aug. 9, 1991 which is a continuation of Ser. No. 07/488,548 filed Mar. 5, 1990 titled Electric Drive for a Segmented Transducer teaches the use of multiresonant generation of nonsinusoidal mechanical stroke wave forms needed for smooth walking. The teachings are primarily directed toward piezoelectric actuators, but are also directed toward electromagnetic actuators that function in a manner similar to piezoelectric ones. The benefits taught are relatively high electrical efficiency derived from resonant excitation of actuator portions, and relatively high electrical stability not normally associated with power amplifiers that drive preponderantly reactive electrical loads. Included in the teachings are the advantages of reactive electrical power sharing between inductive and capacitive portions of the same actuator, resulting in internal reactive electrical power circulation rather than relying on ancillary electrical components.
Many, many background embodiments of resonant traction motors, also referred to as ultrasonic traveling wave motors, are known, for example, Technical Reference EMDUSM-8703 "Ultrasonic Motor", Panasonic Industrial Co., Electric Motor Division of Matsushita Industrial Co. Ltd. Osaka Japan.
This class of motors uses piezoelectric deformations to cyclically sinusoidally excite resonance in an elastic mechanical oscillator such as a ring. One or more surface portions of the oscillator are thereby positioned in an elliptical or circular path. The surface portions cyclically contact the surface of a positioned object or rotor and impart motion thereto by traction. Smooth walking is not achieved by this class of motor because the tangential component of the speeds of the oscillator traction surface portions match the speed of the rotor at at most two relatively small segments of each cycle. Elsewhere in the cycle the mismatch in speed causes traction surface rubbing. Sixty per cent of the available power is transduced to heat due to rubbing in a typical ultrasonic traveling wave motor. Mechanical elastic resonance is predominantly sinusoidal. Relatively high mechanical efficiency is therefore not expected from mechanical resonance traction.
The resonance taught in the applicant's application Ser. No. 07/743,069 filed Sep. 9, 1991 which is a continuation of Ser. No. 07/488,548 filed Mar. 5, 1990 is electrical. The stroke portion contributed by each actuator portion is sinusoidal, is electrically resonant, but not necessarily mechanically resonant. The excitation frequency and amplitude of each actuator portion are predetermined by Fourier rules such that the wave form of the mechanical stroke as measured at the traction member is the algebraic sum of the stroke contributions. This contrasts with the traditional Fourier summing that is done electrically to produce a predetermined and desired electrical wave form that is not sinusoidal. The Electric Drive for a Segmented Transducer application teaches the mechanical wave forms needed to produce smooth walking. Smooth walking results in relatively high mechanical efficiency. Relatively high mechanical efficiency of smooth walking, in combination with the relatively high electrical efficiency of Fourier drive, provides a relatively high actuator system efficiency.
In applicant's copending application Ser. No. 07/697,368 filed May 9, 1991 lifter and tangenter layers are taught using similar rollers but having heat pulses instead of magnetic force as the motivating force.
American Institute of Physics Handbook, 3rd Ed., D. E. Gray, Ed., McGraw Hill Book Co., New York, page 5-33 describes the magnitude and direction of forces mutually acting on two proximate electrical conductors carrying currents. The force F in newtons on one conductor is given as EQU F=2 I.sub.1 I.sub.2 a.sup.-1 .times.10.sup.-7
where I.sub.1 and I.sub.2 are currents in amperes, and a is the distance between conductors in meters.
Culp, G. and Kolin, A., An Intra-Arterial Induction Gauge, IEEE Trans. on Bio-Medical Eng., vol. BME-18, No. 2, March 1971, pp 110-114 describes a relatively accurate method of measuring position by measuring the voltage in a second conductor loop induced by an alternating signal in a first loop, the induced voltage being proportional to the area of both loops.
Attwood, S. S., Electric and Magnetic Fields, 2nd ed., John Wiley and Sons, New York, 1941, Chap. 15 teaches methods of mapping magnetic fields generated by electric conductors proximate magnetically permeable portions, particularly the method of images wherewith the force between the conductor and the magnetically permeable portions is determined in part by assuming that a virtual conductor lies opposite the magnetically permeable portion boundary by the same distance that separates the real conductor from the boundary. Therefore, the function of the magnetically permeable portion may be assumed to be a means of calculating the force due to two currents when only one current is real. Attwood also teaches an increase of magnetic force due to the concentration of magnetic flux by magnetically permeable portions. The relations taught are easily extended to include those cases in which permeable portions are remanent.
"Design and Application of Permanent Magnets," manual no. 6a, Indiana General Corp., Kitchener, Ontario, 1960 teaches the design and application of permanent magnets, including the relationship between force, flux, and air gap reluctance. Therein is made clear the benefit of short mechanical strokes when relatively large forces are desirable, shorter strokes allowing the use of magnetic paths consisting of relatively lower reluctances that allow the generation of relatively large forces. Short mechanical strokes, in the context of the present invention, are those due to small oscillations about a quiescent physical state, as opposed to gross motions such as sliding and full rotations commonly associated with gross motion mechanisms.
"Helenoid Actuators," a brochure of Lucas Industries, N. S. F. Ltd., Ingros Works, Ingrow Lane, Keithley, Yorks BD21 5EF, c. 1980 teaches a relatively wide magnetic circuit having a relatively small cross section area of flux path, stationary conductors, a stationary pole face, and a proximate movable pole face, pole motion being facilitated by ancillary sliding bearings. Conductors participate electrically but are not mechanical agents in forcible positioning.